This invention relates to apparatus for receiving digital signals. More particularly, it is concerned with a digital receiver which is activated by a preparatory digital signal prior to receiving digital information.
In a digital telephone communication system of a certain type during the placing of a call a receiver is assigned to the calling subset and a dial signal is applied to the subset. The subset then produces a digital signal which is designated an interdigit signal. Address code signals are transmitted to the receiver by the subset as by the operation of a key set. The interdigit signal is interrupted by an address code signal but occurs whenever an address code signal is not being transmitted.
In order to insure accuracy of the address code signals received and accepted by the assigned receiver it is desired that the receiver by activated to receive each address code signal only after confirming that the preparatory interdigit signal has been received several times in succession. After activation by receipt of several consecutive words of the interdigit signal the receiver must receive an identical address code word several times in succession before the address code word is accepted as valid.